Restore Accessibility for Dropdown (#16576)

Restore Accessibility for Dropdown (#16576)

* Restore #10096/#8638 and re-fix #15172

This PR restores the vendored and patched dropdow from #8638. It
however, abandons the calls to `click()` using instead the default
dropdown click calls instead. This prevents the issue of the dropdown
grabbing focus permanently however, this may have negative effects on
the effect of focus on the dropdowns.

Of note, the behaviour of the template selector dropdown on the repo
creation page is slightly odd - I don't believe that this odd behaviour
is caused by this PR but rather by the feed source for this. I suspect
that the dropdown should be adding a delete button to its selection.

Fix #15172
References: #7057

Signed-off-by: Andrew Thornton <art27@cantab.net>
* leverage fomantic-build instead

Signed-off-by: Andrew Thornton <art27@cantab.net>
* as per jookia

Signed-off-by: Andrew Thornton <art27@cantab.net>